In a radio communication network, the mode of different radio access technologies operating simultaneously is a common network operation mode. In the network with different radio access technologies operating simultaneously, in order to implement network complementation when different radio access technologies operate simultaneously, handover of services between different radio access technologies is a basic function. Currently, conventional inter-RAT handover flow is: to inform a destination system to prepare radio resources through inter-RAT relocation message, and after the destination system returns relocation response message, initiate the inter-RAT handover flow, thus a handover delay is relatively longer; with regard to a high-speed mobile User Equipment (UE), the handover with a long delay easily causes a dropped call, which influences the handover performance and Quality of Service (Qos).
Iur-g is an interface between an RNC and a BSC, an inter-RAT handover optimization flow based on the Iur-g interface is disclosed in certain enterprise standards currently (with reference to FIG. 1), a radio resource allocation flow of a destination system is advanced before an inter-RAT relocation flow, an air-interface handover flow and the inter-RAT relocation flow are performed in parallel, thereby enhancing an inter-RAT handover success rate and reducing an inter-RAT handover delay. However, since an encryption node of the PS service in the 2nd Generation (2G) communication system is a Servicing GPRS Support Node (SGSN), and a 2G radio access network does not know the encryption situation, therefore, the optimization flow is only applied to the CS handover.
In a dual mode RNC, since the Radio Network Controller (RNC) in the 3rd Generation (3G) communication system and the Base Station Controller (BSC) in the 2nd Generation (2G) communication system are combined into one, and information between dual mode radio access networks can be interacted inside the dual mode RNC.